1. Field of the Invention
The present invention relates to an electronic control apparatus in which an electronic control device is housed inside a sealed casing in an automobile, a motorcycle, an outboard motor, etc.
2. Description of the Related Art
In an electronic control apparatus of this kind, when used under conditions in which a temperature difference inside and outside the casing is great, for example, there has been a risk that the air inside may expand or contract, thereby deforming the casing and leading to damage to a seal portion. Thus, conventionally, a preventive construction has been adopted in which an air vent is formed in a surface of the casing, and a gas-permeable membrane that shuts off passage of liquids and permits passage of gases is disposed so as to cover the air vent. By adopting this preventive construction, if a temperature difference arises inside and outside the casing, air flows through the gas-permeable membrane, an activity called “breathing”, preventing buildup of pressure differences due to expansion and contraction of the air inside the casing, whereby deformation of the casing is prevented preemptively and damage to the seal portion does not occur.
However, one problem has been that if water, etc., adheres to the gas-permeable membrane and freezes, the gas-permeable membrane may lose permeability and become unable to breathe.
In view of this situation, an electronic control device has been proposed in which an air vent is formed in the casing, a gas-permeable membrane that shuts off passage of liquids and permits passage of gases is disposed so as to cover the air vent, a hood is disposed so as to be aligned generally horizontally so as to cover a vicinity of the gas-permeable membrane, an auxiliary air vent is opened though a peripheral wall below the hood, and a protective wall is disposed around the hood so as to be aligned generally horizontally. (See Patent Literature 1, for example.)
In the conventional electronic control apparatus described in Patent Literature 1, the protective wall is formed so as to have a cylindrical shape, an inner surface of an upper peripheral wall is formed so as to have an inclined shape sloping downward inside, and grooves are opened in a lower peripheral wall. Thus, even if water, etc., flows over wall surfaces of the protective wall from outer surfaces of the upper wall to inner surfaces thereof, the water, etc., flows down and inward over an inner surface of the inclined shape, and then flows downward inside the protective wall, and is discharged externally by the grooves. In this manner, the problem of the gas-permeable membrane losing permeability due to water, etc., accumulating inside the protective wall, adhering to the gas-permeable membrane, and freezing is prevented from arising.
Patent Literature 1: Japanese Patent Laid-Open No. 2001-332871 (Gazette)
An electronic control apparatus of this kind is made with a view to preventing deterioration in permeability of the gas-permeable membrane resulting from water, etc., that has entered inside the protective wall as a main objective, and no consideration has been given to problems such as tools, etc., contacting the protective wall and causing damage to the protective wall during mounting.
Specifically, the casing is generally mounted to a boss portion of an engine, for example, by fastening it with bolts, etc. Mounting of the casing is work in an environment surrounded by machinery, and tools such as spanners, wrenches, etc., employed in the fastening of the bolts may strike the protective wall.
In conventional electronic control apparatuses, the protective wall is disposed upright on a surface of the casing, and an outer peripheral surface is formed so as to have a cylindrical shape that is perpendicular to the surface of the casing. Thus, one problem has been that the outer peripheral surface of the protective wall takes the mechanical shock when tools strike the protective wall without mediation, damaging the protective wall, and in the worst cases, damaging the casing.
Damage to the protective wall may lead to exposure of and damage to the hood, and in the worst cases, the gas-permeable membrane may be damaged. If the casing is damaged, the seal on the casing may be lost.